When cleansing water of the colloids and dissolved phosphates therein, there is used a flocculating agent, i.e. a substance which forms flocs which bind thereto and/or therein colloids and dissolved phosphates. These flocculating agents most comprise aluminium and iron salts, such as aluminium sulphate, iron sulphate, iron chloride or mixtures thereof, such as polynucleate aluminium hydroxide complexes of the sulphate or chloride type, these substances when dissolved in water forming metal hydroxide flocs, which constitute the active flocs. Such substances are used for purifying drinking water and sewage water; in this latter case, the water purifying process may also be combined with a biological purifying process. Processes which use flocculating agents are called chemical purification processes.
Normally, the flocculating agent is distributed in the input water in concentrate form, this concentrate often being prepared on site, at the respective water purifying plant, from a highly concentrate form or solid product (BOLIDEN.RTM. ALS, BOLIDEN.RTM. AVR). The agent is distributed by introducing the same in droplet form into a stream of ingoing water, or by introducing the flocculating agent into a large mixing vessel provided with agitating means.
The time taken for each molecule of flocculating agent to disperse in the body of water being treated is so long, however, that the precipitating effect of the agent is not utilized to the full.
It has been established that a flocculating agent passes through three phases in producing its effect. The first phase, which is referred to here as the orthokinetic phase, takes a minimum of 10.sup.-6 seconds to complete, Normally, however, this time period can extend from 30 to 60 minutes in a conventional water purification plant. There are no known methods or apparatus with which this distribution time can be shortened.
Consequently, there is a need to reduce to a minimum the time taken for a flocculating agent to be distributed throughout a body of water under treatment.